CATV networks supply and distribute high frequency “downstream” signals from a main signal distribution facility, known as a “headend,” to premises (e.g., homes and offices) of subscribers. The downstream signals can be provided to subscriber equipment, such as televisions, telephones, and computers. In addition, most CATV networks also receive “upstream” signals from subscriber equipment back to the headend of the CATV network. For example, a set-top box can send upstream signals including information for selecting programs for viewing on a television. Also, upstream and downstream signals are used by personal computers connected through the CATV infrastructure to the Internet. Further, voice over Internet protocol (“VOIP”) telephones use upstream and downstream signals to communicate telephone conversations.
CATV networks use filters and other components to reduce or eliminate unwanted signals that enter the CATV network from external sources, such as subscriber equipment. These undesirable external signals, known as “ingress noise,” can degrade valid CATV signals and general quality of the CATV network. The most intense range of undesirable ingress noise is in the frequency band of 0 megahertz (“MHz”)-15 MHz. This range overlaps those of valid upstream CATV signals, which have a frequency band of 5 MHz-42 MHz. Because the undesirable ingress noise and valid upstream signals can occupy the same frequency band and originate from approximately the same location, it is extremely difficult to filter undesirable ingress noise from valid upstream signals.
Additionally, because valid downstream CATV signals are within a frequency band of 54 MHz-1000 MHz, the ingress noise frequency band of 0 MHz-15 MHz does not overlap and can be suppressed by downstream filters. Even so, the ingress noise can still have adverse influence on the valid downstream signals because ingress noise from individual subscribers accumulates as a substantial underlying level of base noise on the CATV network. To distinguish valid CATV signals from the base noise, the valid CATV signals are typically amplified above the base noise level. However, a high level of base noise may cause signal amplifiers to clip or distort both the valid downstream and upstream signals during amplification and retransmission of those signals, which reduces the information contained in those valid signals, and thereby diminishes the quality of service experienced by subscribers.